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Abstract:

By using the delay profile created by delay profile creating section 102
and the first threshold value 330 received from the first threshold value
calculation 105, the first threshold value timing detection section 103
selects only the earliest receive timing exceeding the first threshold
value, from all the timing that the correlation value in the delay
profile becomes a maximum. By using the receive timing and the second
threshold value 331 received from the second threshold value calculation
section 107, reference timing calculation section 106 selects the
reference timing required for calculating the receive timing for the
incoming wave of the minimum propagation delay time. The timing delayed
by previously set timing behind said reference timing is sent from
receive timing calculation section 108 as the receive timing 113 of the
incoming wave of the minimum propagation delay time.

Claims:

1. A position measuring device which measures a position of a signal
transmitting device, comprising:a delay profile calculating unit which
creates a delay profile representing a correlation between a
predetermined code and a signal which is received by a signal receiving
device;a received timing calculating unit which determines an incoming
wave determination timing which is used to determine a reception of a
particular incoming wave transmitted by said signal transmitting device
in said signal receiving device and that is a point in time when a value
of said delay profile becomes equal to a first threshold, determines a
rising timing when said delay profile rises from a noise level and that
is a point in time when each value of said delay profile becomes equal to
a second threshold which is lower than said first threshold before said
incoming wave determination timing, and determines each received timing
when said signal receiving device receives said signal as to said
incoming wave with reference to said rising timing; anda positioning unit
which calculates each distance between a plurality of said signal
receiving devices and said signal transmitting device on the basis of
said received timing and measures said position of signal transmitting
device from said distances.

2. The position measuring device according to claim 1, wherein said first
threshold value and said second threshold value are set on the basis of a
maximum correlation value in said delay profile.

3. The position measuring device according to claim 2,wherein said first
threshold value is obtained by multiplying said maximum correlation value
by a first predetermined coefficient, andwherein said second threshold
value is obtained by multiplying said maximum correlation value by a
second predetermined coefficient.

4. The position measuring device according to claim 1, wherein said first
threshold value and said second threshold value are set on the basis of a
noise value in said delay profile.

5. The position measuring device according to claim 4,wherein said first
threshold value is obtained by multiplying said noise value by a first
predetermined coefficient, andwherein said second threshold value is
obtained by multiplying said noise value by a second predetermined
coefficient.

6. The position measuring device according to claim 1, wherein said
received timing is delayed by a predetermined time behind said rising
timing.

7. The position measuring device according to claim 1, wherein said
positioning unit calculates said distance on the basis of time difference
between said received timing and a point of time when said signal
transmitting device transmits said signal.

8. A position measuring method comprising the steps of:creating delay
profiles each representing a correlation between a predetermined code and
each of signals which a plurality of signal receiving devices receive by
calculating a correlation value between said predetermined code and each
of said signals;determining each incoming wave determination timing which
is used to determine a reception, in each of said signal receiving
devices, of a particular incoming wave transmitted by said signal
transmitting device and that is a point in time when each value of said
delay profiles becomes equal to a first threshold;determining each rising
timing when each of said delay profiles rises from a noise level and that
is a point in time when each value of said delay profiles becomes equal
to a second threshold which is lower than said first threshold before
said incoming wave determination timing;determining each received timing
when each of said signal receiving devices receives said signal as to
said incoming wave with reference to said rising timing;calculating
distances between each of said signal receiving devices and said signal
transmitting device on the basis of said received timing; andmeasuring
said position of signal transmitting device from said distances.

Description:

CROSS REFERENCES

[0001]This is a continuation application of U.S. Ser. No. 11/976,979,
filed Oct. 30, 2007, which is a continuation application of U.S. Ser. No.
11/059,407, filed Feb. 17, 2005(now U.S. Pat. No. 7,609,197), which is a
continuation application of U.S. Ser. No. 10/680,089, filed Oct. 8, 2003
(now U.S. Pat. No. 6,900,753), which is a continuation application of
U.S. Ser. No. 10/166,090, filed Jun. 11, 2002 (now U.S. Pat. No.
6,657,579, which is a continuation application of U.S. Ser. No.
09/640,018, filed Aug. 17, 2000 (now U.S. Pat. No. 6,459,402). The entire
disclosures of all of the above-identified applications are hereby
incorporated by reference.

BACKGROUND OF THE INVENTION

[0002]The present invention relates to terminal equipment for measuring
its own position, particularly to equipment for measuring distances and
positions using the radio waves emitted from, base stations fixed on the
ground, including CDMA base stations.

[0003]The principles of distance measurement using a spread spectrum
signal are described using FIG. 9. The station for transmitting the
spread spectrum signal transmits this signal in send timing 400. The
aforementioned receiving station receives the spread spectrum signal and
obtains receive timing 401. Differential time 402 between receive timing
401 and send timing 400 is detected as the propagation time of the spread
spectrum signal. The distance between the transmitting station and the
receiving station can be calculated by multiplying differential time 402
by the velocity of light. Because of the principles described above,
distance measurement using a spread spectrum signal requires the
measurement of receive timing 401 at the receiving station.

[0004]Next, the principles of position measurement using a spread spectrum
signal are described. The distances to individual transmitting stations
are measured by the receiving station, subject to the principles
described above. The use of the thus-obtained distances between the
receiving station and each base station and of the positions of the base
stations enables the position of the receiving station to be detected by
solving the equation where the position thereof is taken as an unknown
quantity. Details of one such detection method are disclosed in, for
example, Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995).

[0005]To use spread spectrum signals for conducting distance or position
measurements in this way, it is necessary to measure the receive timing
of the aforementioned spread spectrum signal at the terminal equipment.
In Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995), the
following method for measuring such receive timing is disclosed: the
correlation values between the received signal and the predetermined code
series for creating spread spectrum signals (hereinafter, collectively
called the PN code) are calculated for each receiving event, and a
profile is created that shows the values corresponding to the correlation
values in each receiving event (hereinafter, this profile is called the
delay profile); wherein an epitomized diagram of the delay profile is
shown as 1 in FIG. 10, and the timing where the correlation value becomes
a maximum in the delay profile is searched for and the corresponding
timing is detected as the timing in which the spread spectrum signal is
received. In the example of FIG. 10, "tprev" is the receive timing.

SUMMARY OF THE INVENTION

[0006]During distance measurement and position measurement, it is
important to measure the receive timing of the signal wave that has first
arrived at the terminal equipment, namely, the incoming wave of the
minimum propagation delay time. Consider the case that as shown in FIG.
11, a plurality of spread spectrum signals from a single spread spectrum
signal transmitting station are passed along different propagation routes
and received at terminal equipment as incoming waves 1 and 2 different in
both propagation delay time and signal intensity. In this case, the delay
profile received takes the shape of delay profile 12, a combination of
delay profiles 10 and 11 corresponding to incoming waves 1 and 2,
respectively. In this case, only receive timing 22 of incoming wave 2 can
be detected with the prior art. In the example of FIG. 11, since incoming
wave 1 has the minimum propagation delay time and is received in timing
21, receive timing for the incoming wave of the minimum propagation delay
time cannot be measured using the prior art. As a result, receive timing
measurement errors occur and this makes accurate distance or position
measurement impossible.

[0007]For these reasons, the use of the present invention enables the
distance between a signal transmitting station and a signal receiving
station to be measured by creating a delay profile from the signal wave
received from the signal transmitting station, then taking the startup
timing of the delay profile as reference timing, and detecting the timing
delayed by a predetermined value behind the reference timing.

[0008]To measure position, it is necessary to calculate the foregoing
reference timing for at least three signal transmitting stations, then
calculate the differences in send timing between the corresponding signal
transmitting stations, and detect the position of the signal receiving
station from the respective relative time differences.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is a structural diagram of terminal equipment, the first
embodiment of the present invention;

[0010]FIG. 2 is a flowchart of the receive timing measurement algorithm
used in the present invention;

[0011]FIG. 3 is a structural diagram of the delay profile creating
section;

[0012]FIG. 4 shows an example of a delay profile;

[0013]FIG. 5 shows the first structural example of the first threshold
value calculation section;

[0014]FIG. 6 shows the second structural example of the first threshold
value calculation section;

[0015]FIG. 7 shows the first structural example of the second threshold
value calculation section;

[0016]FIG. 8 shows the second structural example of the second threshold
value calculation section;

[0017]FIG. 9 is a diagram explaining the principles of distance
measurement;

[0018]FIG. 10 is an epitomized diagram of a delay profile;

[0019]FIG. 11 is an epitomized diagram of the delay profiles created when
two incoming waves are present.

DETAILED DESCRIPTION OF THE INVENTION

[0020]The receive timing measurement algorithm used in the present
invention is described using the flowchart shown in FIG. 2, and an
example of the delay profile shown in FIG. 4.

[0021]In first step 500, the correlation value between the received wave
and the PN code is calculated and delay profile 202 is created.

[0022]In step 501, threshold value 206 required for making a distinction
between incoming waves and noise (hereinafter, this threshold value is
called the first threshold value) is calculated in delay profile 202. At
this time, if in delay profile 202, the correlation value exceeds the
first threshold value 206, this threshold value is used to judge that an
incoming wave is present in the particular timing, and this threshold
value is sufficiently greater than the noise level.

[0023]In step 502, among all the timing that the correlation value becomes
equal to the foregoing first threshold value 206, only the earliest
receive timing 205 is detected (hereinafter, the earliest receive timing
is called the first threshold value timing).

[0024]In step 503, threshold value 207 required for detecting the timing
in which the delay profile corresponding to the incoming wave is
calculated (hereinafter, this threshold value is called the second
threshold value). At this time, the second threshold value 207 is used to
detect the timing in which the delay profile is started up from the noise
level, and this threshold value is practically equal to the noise level.

[0025]In step 504, among all the timing that the correlation value becomes
equal to the foregoing second threshold value 207, only the receive
timing 208 closest to and earlier than the first threshold value timing
205 is detected as reference timing. Reference timing 208, therefore,
denotes the timing in which the delay profile corresponding to the
incoming wave is started up from the noise level.

[0026]In step 505, the timing 210 delayed by predetermined value 209
behind the aforementioned reference timing 208 is calculated as reference
timing. This means that the incoming wave has arrived at the receiving
station in receive timing 210. Theoretically, predetermined value 209,
under its noiseless state, has a tip value of 1.0. In actuality, however,
since noise exists, an edge subsequent to the true leading edge is
detected as rise timing. This timing difference should therefore be
subtracted to obtain a value from about 0.7 to 1.0.

[0027]During position measurement that uses spread spectrum signals, when
this measuring method, as with one shown in Japanese Laid-Open Patent
Publication No. Hei 7-181242 (1995), is to be used to conduct
measurements using the relative distance differences between each
transmitting station and the receiving station, step 505 can be omitted
and, instead, the reference timing 208 obtained in step 504 can be taken
as receive timing 210.

[0028]The construction of the terminal equipment, one embodiment of the
present invention, is shown in FIG. 1. The spread spectrum signal that
has been received by antenna 100 is sent to signal receiving section 101,
where the signal then undergoes high/medium-frequency receiving and
baseband signal demodulation. The spread spectrum signal, after
undergoing processing in signal receiving section 101, is further send to
delay profile creating section 102. The correlation value between the
received spread spectrum signal and the PN code is calculated for each
receiving event by delay profile creating section 102, which then creates
a delay profile that shows the values corresponding to the correlation
values in each receiving event.

[0029]A structural example of delay profile creating section 102 using a
matched filter is shown in FIG. 3. In FIG. 3, matched filter 200
calculates the correlation value between the received spread spectrum
signal and the PN code created by PN code generator 201, and sends to
signal line 110 the value corresponding to the correlation value. An
example of a delay profile created by delay profile creating section 102
is shown as solid line 202 in FIG. 4. In FIG. 4, horizontal axis 212
denotes receive timing and as the delay profile bring closer to the left
of the horizontal axis, the receive timing becomes earlier, that is, the
propagation delay time decreases. Vertical axis 213 in FIG. 4 denotes
correlation values.

[0030]The delay profile that has been created by delay profile creating
section 102 is then held in delay profile holding section 115. Delay
profile holding section 115 can be, for example, a memory. The delay
profile, after being held in delay profile holding section 115, is sent
to the first threshold value timing detection section 103, the first
threshold value calculation section 105, reference timing calculation
section 106, and the second threshold value calculation section 107.

[0031]The first threshold value calculation section 105 calculates the
threshold value to be used for the first threshold value timing detection
section 103. A structural example of the first threshold value
calculation section 105 is shown in FIG. 5. In this figure, the maximum
value searching section 300 sends the maximum correlation value (existing
in receive timing 203) of the delay profile received via signal line 110.
Multiplier 320 multiplies the maximum correlation value 310 and
coefficient C0 and sends the results to the first threshold value
timing detection section 103 as the first threshold value 330.
Coefficient C0 is set to about 0.1. This avoids the likely
mis-recognition of a side lobe caused by the characteristics of the band
limiting filter within signal receiving section 101 during the creation
of a delay profile; the side lobe being equivalent to a maximum
correlation value 310 of about 0.1 in terms of magnitude.

[0032]Another structural example of the first threshold value calculation
section 105 is shown in FIG. 6. In this figure, noise power estimating
section 301 estimates noise power using the delay profile received via
signal line 110, and generates an output of noise power 311. The
following two methods are available to measure noise power:

[0033](1) Approximating all received signal power to noise power

[0034](2) Creating a profile repeatedly and calculating the dispersion in
the peak correlation values of the profiles

[0035]Method (2) above, although higher than method (2) in accuracy,
requires a long measuring time. Method (1) above, therefore, is used in
FIG. 6.

[0036]Multiplier 320 multiplies the abovementioned noise power 311 and
coefficient C1 and sends the results to the first threshold value
timing detection section 103 as the first threshold value 330.
Coefficient C1 is set to a value from about 10 to 100 for this
reason: when the noise is considered to be white noise, momentary
amplitude changes in accordance with the required distribution, and in
this case, if the noise power is taken as the square of σ, the
probability where the momentary amplitude exceeds 3σ is about
3/1000, which is sufficiently slow as the probability of an measuring
error occurring, and thus since an amplitude of 3σ is nine times
the square of σ in terms of power, C1 needs only to be more
than nine.

[0037]In FIG. 6, output 116 of signal receiving section 101 can likewise
be used as the input of noise power estimating section 301. Also, the
first threshold value calculation section 105 can have the structural
components shown in both FIGS. 5 and 6, and send the greatest of the
threshold values calculated thereby, to the first threshold value timing
detection section 103 as the first threshold value 330. Or the first
threshold value calculation section 105 can have the structural
components shown in both FIGS. 5 and 6, and send the smallest of the
threshold values calculated thereby, to the first threshold value timing
detection section 103 as the first threshold value 330.

[0038]The first threshold value 330 received from the first threshold
value calculation section 105 is used for the first threshold value
timing detection section 103 to generate the earliest receive timing in
which the correlation value becomes equal to the first threshold value
330. The operation of the first threshold value timing detection section
102 is described using FIG. 4. In FIG. 4, discontinuous line 206
represents the first threshold value 330 received from the first
threshold value calculation section 105. The earliest receive timing 205
that, in delay profile 202, the correlation value becomes equal to
threshold value 206 is sent from the first threshold value timing
detection section 103 to signal line 111.

[0039]The second threshold value calculation section 107 calculates the
threshold value to be used for reference timing calculation section 106.
A structural example of the second threshold value calculation section
107 is shown in FIG. 7. In this figure, the same components as those
shown in FIG. 5 as the first structural example of the first threshold
value calculation section 105, are each assigned the same number as that
of each shown in FIG. 5. Multiplier 320 multiplies the maximum
correlation value 310 sent from the maximum value searching section 300,
and coefficient C2, and sends the results to reference timing
calculation section 106 as the second threshold value 331. Coefficient
C2 is set to about 0.1, which is based on data that was measured
using an experimental machine.

[0040]Another structural example of the second threshold value calculation
section 107 is shown in FIG. 8. In this figure, the same components as
those shown in FIG. 6 as the second structural example of the first
threshold value calculation section 105, are each assigned the same
number as that of each shown in FIG. 6. Multiplier 320 multiplies the
noise power 311 sent from noise power estimating section 301, and
coefficient C3, and sends the results to reference timing
calculation section 106 as the second threshold value 331. Coefficient
C3 is set to about 7, which is based on data that was measured using
an experimental machine.

[0041]In FIG. 8, output 116 of signal receiving section 101 can likewise
be used as the input of noise power estimating section 301. Also, the
second threshold value calculation section 107 can have the structural
components shown in both FIGS. 7 and 8, and send the greatest of the
threshold values calculated thereby, to reference timing calculation
section 106 as the second threshold value 331. Or the second threshold
value calculation section 107 can have the structural components shown in
both FIGS. 7 and 8, and send the smallest of the threshold values
calculated thereby, to reference timing calculation section 106 as the
second threshold value 331.

[0042]The second threshold value 331 received from the second threshold
value calculation section 107, the receive timing detection results
received from the first threshold value timing detection section 103, and
the delay profile received from delay profile holding section 115 are
used for reference timing calculation section 106 to calculate the
reference timing for obtaining the receive timing of the incoming wave of
the minimum propagation delay time. The operation of reference timing
calculation section 106 is described using FIG. 4. In FIG. 4, single-dot
dashed line 207 represents the second threshold value 331 received from
the second threshold value calculation section 107. Reference timing
calculation section 106 compares the correlation value and threshold
value 207 in the receive timing 205 that has been received from the first
threshold value timing detection section 103. If both values mismatch,
the receive timing is advanced and the correlation value and threshold
value 207 in said receive timing are compared. This sequence is repeated
until the correlation value and threshold value 207 have matched, and the
corresponding receive timing is sent as an output. In the example of FIG.
4, receive timing 208 in which the correlation value and threshold value
207 match is sent as reference timing to signal line 112.

[0043]The reference timing received from reference timing calculation
section 106 via signal line 112 is used for receive timing calculation
section 108 to calculate the receive timing for the signal wave that has
first arrived at the terminal equipment, namely, the incoming wave of the
minimum propagation delay time. The operation of receive timing
calculation section 108 is described using FIG. 4. Timing 210 delayed by
previously set timing 209 behind the reference timing 208 that has been
sent from reference timing calculation section 106 is detected as the
receive timing for the wave of the minimum propagation delay time, and
the detected receive timing is then sent to signal line 113.

[0044]The above method when applied to delay profile 12 shown in FIG. 11
is described. The first threshold value timing detection section can send
receive timing 24 by using the appropriate first threshold value 330.
Next, the reference timing calculation section can send receive timing 20
by using the appropriate second threshold value 331. Furthermore, receive
timing calculation section 108 can detect receive timing 21 by first
measuring beforehand, under an environment having only one incoming wave,
timing difference 23 between all values from the startup timing of the
delay profile to the maximum value thereof, and then using said timing
difference 23 in receive timing calculation section 108. Receive timing
21 is the receive timing for incoming wave 1, the signal wave that has
first arrived. In other words, even if two incoming waves are received in
overlapping form, it is possible to detect the receive timing for the
signal wave that has first arrived.

[0045]Based on the receive timing 113 sent from receive timing calculation
section 108, calculations for distance measurement or position
measurement are performed by distance/position measuring section 114.
Distance/position measuring section 114 can use, for example, the method
disclosed in Japanese Laid-Open Patent Publication No. Hei 7-181242
(1995).

[0046]During position measurement that uses spread spectrum signals, when
this measuring method, as with one shown in Japanese Laid-Open Patent
Publication No. Hei 7-181242 (1995), is to be used to conduct
measurements using the relative distance differences between each
transmitting station and the receiving station, processing by receive
timing calculation section 108 can be omitted and, instead, output 112 of
reference timing calculation section 106 can be connected to signal line
113 and the corresponding output value can be sent to distance/position
measuring section 114. In this case, delay profiles are created using the
signal waves received from at least three signal transmitting stations,
and then the first and second threshold values are created for each such
delay profile. Subsequently, the startup timing of each delay profile is
detected and the differences in send timing between the corresponding
signal transmitting stations are used for the receiving station to
measure its position from the relative time differences between the
signal transmitting stations.

[0047]The present invention enables accurate detection of the receive
timing for the first incoming wave arriving under the multi-path
environment that a plurality of incoming waves are received in
overlapping form. Thus, it is possible to minimize measurement errors at
the terminal equipment that uses spread spectrum signals to conduct
distance and position measurements.